The development of vascular heterogeneity is marked by regional changes in vascular morphology associated with alterations in cellular gene and protein expression. The ability to measure these changes at the single celt level is therefore crucial to investigate the mechanisms underlying the development of vascular heterogeneity. The goal of this Core is to provide the investigators of this proposal with a means of studying alterations in vascular development using state-of-the-art histochemical, immunohistochemical and gene expression analysis. All of the projects in this proposal will generate mice in which the function of a putative regulator of vascular development has been altered to study its role in vivo. This core will be responsible for processing the tissues of these animals and for their complete histologic analysis. This core is well-established and has generated a large percentage of the preliminary data in this proposal and contributed to numerous publications by the participating investigators. This core will provide a uniform, high level of quality for the proposed studies and the expertise to develop new methods that will be shared among the investigators.